Field of the Invention
The present invention relates to an optical positional information detection apparatus and an object association method.
Description of the Related Art
There are electronic white boards in which an information acquisition function, a display function, a communication function, and the like are added to a white board of related art. Information written on the electronic white board by a user is stored as coordinate data and the electronic white board renders the information on a display surface of a display. Accordingly, the user can draw characters or figures in the same manner as in a white board of related art. Further, the user can utilize drawing data by saving the drawing data or transmitting the drawing data to another electronic white board, for example.
One of methods by which the electronic white board obtains coordinates input by the user is an optical method. FIG. 1A schematically shows features of an optical coordinate detection method. Imaging units 32a and 32b are disposed at an upper left corner and an upper right corner of a display 200. The user uses an electronic pen that includes a light-emitting unit at a pen tip, the finger without the light-emitting unit, or a pen-shaped member (hereafter an “indication member”) to draw characters or figures on the display 200. The electronic white board captures an image of the indication member using the two imaging units 32a and 32b and calculates coordinates of the indication member on a display surface of the display 200 based on triangulation. The indication member captured by the imaging units 32a and 32b is referred to as a target. In FIG. 1A, one target 1 is captured.
On a touch panel, it is possible to simultaneously detect a plurality of locations touched by the fingers or the like. With respect to the electronic white board, there is a demand for simultaneous use of indication members by a plurality of users or a demand for simultaneous use of a plurality of indication members by a single user.
However, when the plurality of indication members are to be used simultaneously, the electronic white board may detect a ghost point. The ghost point refers to detection or coordinates of the indication member at a location where there is no actual indication member. When the ghost point is detected, the electronic white board does not respond correctly (for example, a drawing point may be drawn at a location different from a location of writing with the indication member or an appropriate response may not be obtained when a plurality of fingers are used for operation).
The ghost point is described with reference to FIG. 1B. There are two targets 1 and 2 on the display surface of the display 200. In this case, a ghost point g1 appears on a point of intersection between a straight line connected to the imaging unit 32a and to the target 1 and a straight line connected to the imaging unit 32b and to the target 2. A ghost point g2 appears on a point of intersection between a straight line connected to the imaging unit 32a and to the target 2 and a straight line connected to the imaging unit 32b and to the target 1.
There have been suggestions of techniques that eliminate such a ghost point (see Patent Document 1, for example). Patent Document 1 discloses a method for preventing detection of ghost points by estimating a current location of a target whose past location and speed are input in a Kalman filter or the like.
However, in the method disclosed in Patent Document 1, if locations of two targets are close to each other when seen from one imaging unit, for example, a ghost point may be detected because it is difficult to track the targets while identifying the targets.
[Patent Document 1] Japanese Translation Publication No. 2011-522332 of PCT International Application